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Biomedical subjects

F Nüsslin

Publications and source records attributed to F Nüsslin.

At least 19 recordsLinked to original sources
PubMed1996

Treatment planning for bicentric stereotactic irradiation.

We have investigated a bicentric stereotactic convergent beam irradiation technique for the treatment of irregularly shaped, especially elongated, target volumes. Depending on the size and shape of the target volume optimum values for the isocenter distance, collimator apertures and dose inhomogeneity have been determined which serve as starting parameters for the interactive optimization of dose distribution. The treatment planning system of the stereotactic unit SRS-200 (Philips) has been used to calculate the parameter tables. However, the presented results are also applicable to other stereotactic systems.

Film Dosimetry↗
PubMed1996

Quality assurance in radiotherapy: the importance of medical physics staffing levels. Recommendations from an ESTRO/EFOMP joint task group.

The safe application of ionising radiation for diagnosis and therapy requires a high level of knowledge of the underlying processes and of quality assurance. Sophisticated modern equipment can be used effectively for complicated diagnostic and therapeutic techniques only with adequate physics support. In the light of recent analyses and recommendations by national and international societies a joint working group of representatives from ESTRO (European Society for Therapeutic Radiology and Oncology) and from EFOMP (European Federation of Organisations for Medical Physics) was set up to assess the necessary staffing levels for physics support to radiotherapy. The method used to assess the staffing levels, the resulting recommendations and examples of their practical application are described.

Europe↗
PubMed1995

Does the photon beam quality factor depend on the type of ionization chamber?

The photon beam quality factor Q of 6- and 15-MV photon beams has been measured using different types of thimble ionization chambers with various wall, electrode and insulator materials. Some types of chambers seem to overestimate the corresponding Q-value by 0.4% (6 MV) and 0.7% (15 MV), respectively. The effect on the stopping power ratio water to air and on the pertubation correction will be discussed.

Photons↗
PubMed1995

Influence of the administered mass of tellurium on plasma clearance in rabbits.

The combination of analytical techniques such as PNA and SIMS with a compartmental approach enables the study of the metabolism and biokinetics in humans of several elements by using stable isotopes as tracers. The techniques developed for Te require the administration of greater masses than those used for similar studies performed with radioactive tracers, therefore a test was carried out in rabbits in order to assess the possible influence of the administered amounts on the determination of the biokinetic parameters. The behaviour of the tracers was found to be similar for Te administration of up to 70 micrograms/kg of body weight. An inter-individual variability in the size of the transfer compartment was observed and has to be taken into account.

Animals↗
PubMed1995

[Bicentric stereotaxic convergent-beam irradiation].

PURPOSE: Circular collimated X-ray beams rotated in various non-coplanar planes as commonly used in stereotactic linac-based radiotherapy are generating spherical dose distributions with typically steep dose gradients. In case of irregular, especially elongated lesions, this technique fails to conform the shape of the corresponding planning target volume, and a collimator aperture has to be selected which allows for an acceptable dose distribution only on the expense of an excess dose to a larger amount of normal tissue. Therefore we have investigated a bicentric irradiation technique with sequentially treating an elongated target volume over two separated isocenters. METHODS: For the computer simulation studies we used the planning system of the stereotactic unit SRS-200 by Philips. Selected combinations of different collimator aperture were examined systematically by varying the distance between the two isocenters. Dose distributions for a specially developed head-phantom were calculated and analysed. RESULTS: Optimization tables were generated taking into account the geometric quality criteria as well as the corresponding dose maxima. For a given size of the target volume, the appropriate parameters for the bicentric radiation treatment can be chosen. The calculated dose distributions turned out to be independent of the positioning of the two isocenters within the phantom. CONCLUSION: The optimization tables serve to select a set of starting values for the interactive planning process of an elongated target volume resulting in a significant decrease of the overall time for treatment planning of irregular shaped lesions.

Film Dosimetry↗
PubMed1995

[Relations between physician and physicist. Remarks from the viewpoint of the physicist].

BACKGROUND: Complication-free cooperation between physicians and physicists is widely to be found in all areas of biomedical research for a long time. Where both are involved in patient care, however, there are interfaces potentially causing frictions in their relationship. Radiotherapy is considered to be a typical example. KEY ISSUES FOR GOOD RELATIONSHIP: In order to establish a partnership free of tensions 5 attitudes are felt to be essential: interdisciplinary cooperation, recognized professional competency, mutual loyalty among colleagues, actively supported communication, and readiness for conciliation. CONCLUSION: Considering the interdisciplinary attitude of biomedical science as well as appreciating the ethical obligation to the patient good partnership between physician and physicist is necessary and achievable.

Ethics, Medical↗
PubMed1991

New device for CT-targeted percutaneous punctures.

A device for computed tomography (CT)-guided percutaneous punctures that is not affixed to the patient and can be used even when the gantry is tilted was developed and tested. In initial patient examinations, the device was accurate within 1.0 mm of the predetermined target point. Experience so far has involved retrobulbar anesthesia and puncture of intervertebral disk space.

Anesthesia, Local↗
PubMed1991

[Computer-assisted irradiation planning in whole-body irradiation].

Using a commercial system designed for external beam radiation treatment planning a simple method is described for calculating dose distribution in total body irradiation. Scaling factors are applied to keep the range of all distances within the limits preset for the routine use of the planning system. As an example the validity of the method is tested in the lung region which due to dose inhomogeneities is especially critical to an accurate dose determination. Comparing dose calculation and phantom measurements reasonable agreement is obtained.

Humans↗
PubMed1990

TBI technique and clinical results of leukemia patients at the University of Tübingen.

Since 1976, more than 180 patients suffering from leukemia or aplastic anemia have been treated with BMT and TBI. The improvement of TBI-technique starting from single fraction irradiation without any shielding to different types of fractionation schemes with lung, head and neck shielding and an electron boost to the thoracal wall is shown. A more detailed description of the actual TBI-technique is given; this has been applied to 64 patients to-date. Some clinical results are summarised into four subgroups. Life table analyses are shown for single fraction irradiation as well as for fractionated irradiation separated for high and for low risk patient groups.

Anemia, Aplastic↗
PubMed1990

[Water-energy dosage calibration and standard ion dosage calibration--a comparison in ultrahard x-ray radiation].

Ten ionization chambers (PTW), partly of different type, which all have been calibrated in terms of absorbed dose to water, were used to compare the absorbed dose indicated in a reference geometry at 8 MV X-rays. The standard deviation of the mean value of the absorbed dose determined for all chambers was 0.5%. Since 4 chambers have been calibrated in terms of absorbed dose to water and in exposure, the absorbed dose to water was determined from indicated value according to both calibration procedures. The dose values obtained via the energy dose calibration turned out to be about 2.5% less compared to the result when applying the exposure calibration factor.

Calibration↗
PubMed1990

[2 years' experience with a monitoring and recording system for gynecological afterloading irradiation].

A computer program running on a simple desk calculator has been developed for monitoring and recording gynecological high-dose afterloading therapy. For treatment monitoring the multiple-probe AM6-system (PTW-Freiburg) is used which allows for dose measurements in the urinary bladder and the rectum. The probe signals are processed on line in order to indicate the actual dose at the measuring points. After completing the irradiation the treatment is documented. Performing fractionated treatment the measuring data are stored in the computer memory for calculating total accumulated dose. The above-described monitoring and recording [correction of protocolling] system has proven its usefulness during two years of clinical work.

Brachytherapy↗
PubMed1985

[Development of a clinical tumor registry using the DATACORD program package].

During the establishment of a new radiooncologic department in a general hospital, a clinical tumor register has been developed for internal patient documentation. The authors describe the general requirements which had to be fulfilled by this tumor register as well as the reasons leading to the purchase of a commercial program package adapted to an irradiation planning system. The structure of the programs and the specification of characteristics are defined. Finally some aspects of organisation regarding the use of the register are mentioned.

Computers↗
PubMed1985

[Medical and physical aspects of quality assurance in radio-oncology].

A more extensive interpretation of quality control in radio-oncology is opposed to the conception mostly restricted to technical inspections. A review is given of the most important medical and physical aspects of an optimized radiotherapy. Some examples are chosen from the great number of national and international recommendations agreed upon in order to standardize the measures of quality control. Finally some simple radiobiologic models are presented and the corresponding precision requirements are compared with the uncertainties of the dose determination resulting in clinical practice.

Humans↗